(1) Field of the Invention
The present invention relates to an exposure control device for flash photography, especially an exposure control device capable of automatically obtaining a combination of a diaphragm aperture and an exposure time for flash photography in accordance with a light measurement.
(2) Description of the Related Art
When a backlit scene having a central object darker than a surrounding object is photographed with flash light illumination of which the amount is controlled by a flash light emission amount control means, if an optimum exposure is wanted for both the central object and the surrounding object, it is necessary to determine a shutter speed or an exposure time and a diaphragm aperture value for the flash photography taking the brightness of the central object, the brightness of the surrounding object and the difference in brightness between both objects into consideration. Since, however, this determination requires a great deal of skill, flash photography often ends in failure. As a means for overcoming this disadvantage, U.S. Pat. No. 4,550,996, and U.S. Pat. No. 4,558,939 proposed a device having a programmed exposure control for flash photography which determines a combination of an exposure time fixed to a flash synchronizable critical shutter speed and an aperture value changed on a high brightness region in accordance with the brightness of an object to be photographed or fixed on a low brightness region to a predetermined aperture value. If this device is used, even for a backlit scene as described above, an exposure adequate to some extent can be attained, and therefore, a camera provided with this device is suitable for non-skilled beginners.
In this conventional device, however, since flash photography in which the brightness of the surrounding object is taken into consideration is carried out only on a higher brightness side, and the exposure time is fixed to the flash synchronizable critical shutter speed, photography under special conditions, such as flash photography at a low brightness with the brightness of a surrounding object being taken into consideration and at an exposure time lower than the flash synchronizable critical shutter speed, cannot be performed. In order to perform this kind of flash photography, it is necessary for the photographer to manually set the exposure time or aperture value to a desired value. Determination of this desired value is not easy for a beginner to perform such special flash photography. Moreover, in the above-mentioned conventional device, when this kind of flash photography is carried out, it is necessary to change the exposure control mode to the manual mode and provide a setting member for manually setting the exposure time or aperture value to a desired value, and therefore, the structure of a camera becomes complicated. As a result of our research, we found that even in the above kind of flash photography, if the combination of the aperture value and exposure time is selected based on the brightness of an object according to a specific program, satisfactory photos can be usually obtained.
Accordingly, a method may be considered in which the flash photography program of the above-mentioned conventional device is set so that even in the low brightness region, an appropriate combination of the aperture value and the exposure time can be obtained while taking the brightness of a surrounding object into consideration. In this case, however, the exposure time becomes long in the low brightness region, and the possibility of camera shake when the camera is held only by hand is increased and beginners are not likely to realize a satisfactory photograph.